As far as I can tell, Katello 4.18 (which should be the corresponding Katello release to Foreman 3.16) has not yet been released: Katello 4.18.0 Release Process
I am unsure how this could correspond to installer packages/executables getting removed, but in general you should only update Katello stacks once the new Katello version gets released. Running Foreman with incompatible Katello versions is expected to break afaik.